As a general constitution of a head for use in ink jet recording, there can be exemplified a constitution in which a plurality of discharge ports, ink flow paths connected to these discharge ports, and a plurality of electro-thermal conversion elements for generating thermal energy used to jet an ink are provided. Each of the electro-thermal conversion elements has a heating resistor and an electrode for supplying electric power to the heating resistor, and this electro-thermal conversion element is coated with an insulating film to secure insulation between the respective electro-thermal conversion elements. Each ink flow path is connected to a common liquid chamber at an end opposite to the discharge port of the ink flow path, and in the common liquid chamber, the ink supplied from an ink tank as an ink reservoir part is reserved. The ink supplied to the common liquid chamber is led to the respective ink flow paths so that the ink is held forming a meniscus in the vicinity of the discharge port. In this state, the electro-thermal conversion elements are selectively driven to generate thermal energy, and the thus generated energy is then utilized to rapidly heat the ink and to generate bubbles on a thermal action surface, so that the ink is discharged under a pressure caused by such a state change.
The thermal action part of the ink jet head during the ink discharging time is heated by the heating resistor and hence exposed to a high temperature, and simultaneously, the thermal action part combinedly suffers a cavitation impact due to the bubbling and contraction of the ink, and a chemical action of the ink. This chemical action of the ink brings about the following phenomenon. Specifically, color materials, additives and the like contained in the ink are heated at a high temperature, whereby they are decomposed on a molecular level and change into hardly soluble substances, which are physically adsorbed on an upper protective layer. This phenomenon is called kogation. When the hardly soluble organic and inorganic substances are adsorbed on the upper protective layer in this way, thermal conduction from the heating resistor to the ink becomes uneven, and in consequence, the bubbling becomes unstable.
Heretofore, a Ta film which can relatively withstand the cavitation impact and the chemical action of the ink has been formed so as to be a thickness of 0.2 to 0.5 μm, whereby both of life and reliability of the head has been intended.
Referring to FIG. 9, detailed description will be made about a condition caused by the bubbling and bubbling stop of the ink in the thermal action part.
A curve (a) in FIG. 9 shows a change with time of surface temperatures of the upper protective layer from a moment when a voltage is applied to the heating resistor, in a case where a driving voltage Vop=1.3×Vth (Vth represents an ink bubbling threshold voltage), a driving frequency is set to 6 kHz and a pulse width is set to 5 μs. Furthermore, a curve (b) shows a growing state of formed bubbles from a moment when the voltage is applied to the heating resistor in a similar manner. As shown by the curve (a), the rise of the temperature starts from the moment when the voltage is applied, and a temperature rise peak is observed slightly behind a predetermined pulse time (because the heat from the heating resistor slightly late reaches the upper protective layer). Afterward, the temperature mainly lowers due to thermal diffusion. On the other hand, as shown by the curve (b), the growth of the bubble starts from a time when the temperature of the upper protective layer reaches about 300° C., and after the maximum bubbling is reached, the bubbling stops. In the actual head, the above operation is repeated. In this way, the surface temperature of the upper protective layer rises up to, for example, about 600° C. with the bubbling of the ink, which shows that ink jet recording is carried out with the thermal action at the high temperature.
Accordingly, the upper protective layer which comes in contact with the ink is required to have film properties excellent in heat resistance, mechanical properties, chemical stability, oxidation resistance, alkali resistance and the like. As materials for use in the upper protective layer, in addition to the above-mentioned Ta film, noble metals, high-melting point transition metals, alloys of these metals, nitrides, borides, silicides or carbides of these metals, amorphous silicon or the like are known in the prior art.
For example, as described in Japanese Patent Application Laid-Open No. 2001-105596, an upper protective layer is formed on a heating resistor via an insulating layer, in which the upper protective layer is made of an amorphous alloy represented in a composition formula TaαFeβNiγCrδ (wherein 10 at. %≦α≦30 at. %, α+β>80 at. %, α<β, δ>γ, and α+β+δ+γ=100 at. % are satisfied), and a contacting surface thereof with the ink contains an oxide of the component substance, so that a reliable recording head with a longer service life is proposed.
However, in recent years, the needs for higher quality of record images and higher performance such as high-speed recording in ink jet recording apparatuses have been increased, and in order to meet the needs, enhanced ink performance has been required. For example, improved coloring properties and weather resistance have been demanded in order to address the high-quality record images and also the prevention of bleeding (blur between different color inks) has been demanded in order to address the high-speed recording. Consequently, an attempt to add various components to the ink has been made. With regard to the kinds of ink, in addition to black, yellow, magenta, and cyan, a pale color ink obtained by reducing a concentration or the like has been developed, which has brought about diversification of the ink. In some case, there occurs a phenomenon that even the Ta film, which is conventionally considered to be stable as an upper protective layer, corrodes due to thermochemical reaction with the ink. In the case where the ink containing a bivalent metal salt such as Ca and Mg or a component forming a chelate complex is used, the above-mentioned phenomenon remarkably appears.
In order to further speed up the ink jet recording, driving by shorter pulse than ever (that is, driving with a driving frequency increased) is required. In such shorter pulse driving, since the process of heating, bubbling, bubbling stop and cooling in a thermal action part of a head is repeated in a short period of time, the thermal action part is subjected to a larger thermal stress in a shorter period of time as compared to a conventional one. Furthermore, since the shorter pulse driving concentrates cavitation impact arising from the ink bubbling and contraction on an upper protective layer in a shorter period of time than ever, an upper protective layer particularly excellent in mechanical impact property has been demanded.
While these various improvements in the ink have been advanced, a problem has been found that in the case where an upper protective layer with improved corrosion resistance to the ink as described above is formed, using a certain kind of ink may cause a product due to kogation to be remarkably deposited on a heating portion, thereby reducing discharge performance.
Furthermore, as a manufacturing method of a substrate for ink jet with the above-mentioned upper protective layer formed, a process by dry etching is generally used in many cases. However, in the case where the upper protective layer with improved corrosion resistance to the ink is formed, although high durability can be maintained for a long time, it is predicted that a process of forming a desired pattern or the like by etching or the like becomes difficult. FIGS. 8A to 8E illustrate it. As shown in FIGS. 8A to 8E, in pattern formation of the upper protective layer, the process by dry etching generally used in many cases may cause an insulating protective layer contacting the upper protective layer to be etched. If etching selectivity between the insulating protective layer and the upper protective layer could be sufficiently secured as in a conventional substrate, it would be possible to etch the upper protective layer with the insulating protective layer being left. Actually, over-etching at a boundary portion with the upper protective layer may produce a step (between A and B in FIG. 8E). Owing to such a phenomenon, the insulating protective layer becomes thinner at the boundary portion by etching so as to have a film thickness b smaller than a designed film thickness b, which leads to insufficient exertion of a protective function thereof. Therefore, it is necessary to obtain conditions of control based on etching time in consideration of an etching rate of the upper protective layer by an etching gas to etch only the upper protective layer and then to perform patter formation. A problem, however, has been found that since the upper protective layer may be left unetched or, on the contrary, the insulating protective layer may be etched due to unevenness attributed to devices or etching conditions, the pattern formation of the upper protective layer may not be performed stably.